I. Field of the Invention
This invention relates to a one-trip packstock assembly and, in particular, to a whipstock packer assembly having a smaller than usual outer diameter yet capable of effectively packing-off conventional casing diameters.
II. Description of the Prior Art
Well packers are widely utilized to seal or isolate one or more zones in a well hole. Generally, several levels of interest are sealed from each other by a packing arrangement between the well casing and the work string. Packers have also been utilized to orient and support additional tools, such as a whipstock, in order to control the direction of the tool. However, most of the past known packing tools are generally designed to pack-off and seal gaps of 3/16" or smaller. Thus, the initial diameter of the packing device must closely conform to the inner dimensions of the well casing.
Because of the small leeway provided in conventional packing tools, such devices have a tendency to hang-up in the casing as they are lowered therein. This is particularly problematic in casing packers which are run in conjunction with additional tools thereby extending the overall length of the combination tool. As the length of the tool associated with the packer is increased, the ability to maneuver through irregular casing sections is decreased due to the limited leeway between the packer and the casing wall. In order to reduce hang-ups, such multiple tool operations are generally conducted in two trips. The first trip is utilized to run and set the packing device while the second trip positions the working tool, such as a whipstock utilized to sidetrack a well. Since the packing tool was only a few feet long it could easily be maneuvered through the casing. However, the two trip operations resulted in increased costs particularly in very deep well operations. Moreover, while running the whipstock and packer individually is normally a fairly simple procedure, a highly deviated well may require that the packer be run on the drillstring. In this situation, a simple procedure becomes time-consuming and complex.
In order to reduce production costs, a one-trip tool adapted to pack-off gaps of greater than one-half inch was developed. Such a combination tool is described in U.S. Pat. No. 4,397,355 entitled Whipstock Setting Method and Apparatus. The packing tool described therein is adapted to pack-off the increased gap. However, it has been found that because of the larger gap the rubber sealing element has a greater tendency to extrude along both the inner mandrel and the casing wall, thereby causing leakage past the packing element. Pressure packers have also been utilized in an attempt to prevent this leakage. However, these pressure packers would only withstand pressures proportional to the pressure initially put into packers since the pressure supply line is severed upon actuation of the whipstock. Any increase in downhole pressure would cause leakage past the tool.
Thus, the past known tool have failed to effectively seal and pack-off the casing, particularly when extreme well pressures are present.